A semiconductor device continues to be downsized, and in recent years, a semiconductor device having a new structure emerges. Among them, in a memory device using a resistive element and a magnetic element, there is a device that has a non-conventional shape, forms a pillar structure having a diameter of several tens of nanometers or less and stores data in the pillar structure. In addition, also in a logic device, a structure in which a gate is formed around a channel region of a columnar structure is proposed. Hereinafter, this columnar shape is referred to as nanopillar. Some nanopillars have a small aspect ratio, and the nanopillars should be referred to as nanodots in some cases. However, here, the nanopillars are collectively referred to as a nanopillar.
In addition to the semiconductors, in medical use, a device which is formed with nanopillar shapes concentrated in an inspection of cells, blood, or the like may be used in some cases.
In general, top-down observation using a critical dimension scanning electron microscope (hereinafter referred to as CD-SEM) having a length measurement function is introduced for inspection of such a fine pattern. In a case of a semiconductor device, a pattern formed on a Si substrate is observed. In addition, in a case of inexpensive chips such as a chip for medical use, a mold is an object of observation. The reason why the CD-SEM is used is a high magnification of the apparatus and high measurement reproducibility. In mass production plants, it is necessary to automatically adjust a state of the hardware, automate an imaging, and automate processing and output of a result. However, the CD-SEM and surrounding software of the CD-SEM are evolutionally advanced and are responded to these demands.
Not only a critical dimension (hereinafter, referred to as “CD”) but also a slight deviation from design data of a pattern shape has become a problem as the pattern dimension is reduced. Therefore, an index to evaluate an overcome of the pattern shown in an image is proposed, and the function of the CD-SEM is increasing. For example, a fine irregularity of an edge of a line pattern is called line edge roughness, and its measurement function is general.
In also the evaluation of the overcome of the nanopillars, a matter that an image analyzing is performed by performing top-down observation is considered as a method most easy to introduce in the mass production process.
Therefore, a method to evaluate the shape from a top-down observation image of the nanopillar is required.
There are no shape evaluation methods specialized for the nanopillars so far. However, as a method for evaluating the shape of a hole pattern of a semiconductor, PTL 1 and PTL 2 show examples of various indices. A two-dimensional closed curve obtained by top-down imaging of a pattern is approximated by an ellipse, a feature amount such as a major axis direction thereof, a circumferential length of a closed curve or a value obtained by dividing the circumferential length by an area, and an eccentricity of an ellipse is output. In this example, there is an object to detect an abnormality of a pattern forming apparatus (exposure apparatus), and an index which easily detects a distortion in a certain direction and a focus deviation of a transferred image easily caused by an optical lens or the like is described.